(R)-3-hydroxybutyrate (3-HB) is an optically chiral compound with the CAS No. 625-72-9. (R)-3-hydroxybutyric acid is produced by the metabolism of long chain fatty acids in the liver of mammals. It exists as a major ketone in plasma and peripheral tissues and can be used as an energy source in most tissues of the body.
(R)-3-hydroxybutyric acid has positive effect on treating many diseases and nutritional functions as well. For example, it can be used to treat many diseases that arise from elevated levels of ketone (such as nerve disorders including epilepsy and myoclonus, and neurodegenerative diseases including Alzheimer's disease and dementia); it can reduce free radical damage by oxidizing the coenzyme Q (such as ischemia); it can enhance the efficiency of metabolism to achieve the treatment of inadequate support, angina, myocardial infarction, etc. by improving training efficiency and athletic performance; it can also be used to treat cancer related diseases such as brain cancer (astrocytoma, etc.). Further, it has good effects on the treatment of glucose metabolism disorders (such as type-1 diabetes, type-2 diabetes, hypoglycemia ketone disease, etc.). It can be used to control osteopenia (osteopenia), osteoporosis, severe osteoporosis and related fractures. Based on these functions and therapeutic and nutritional effects, (R)-3-hydroxybutyric acid and its salts can be used as food additives and drugs with great health and medicinal values.
(R)-3-hydroxybutyric acid has been prepared primarily by chemical methods. It can be made from direct chemical synthesis or prepared by enzymatic degradation of poly-3-hydroxybutyrate with poly-3-hydroxybutyric acid depolymerase. The chemical synthesis of (R)-3-hydroxybutyric acid requires a high temperature, a high pressure and expensive chiral metal catalysts. The process of enzymatic degradation of poly-3-hydroxybutyric acid requires a large amount of organic solvent, and very pure poly-3-hydroxybutyrate as starting material. Besides the long reaction time, it is difficult to control the racemization of product after reaction. Moreover, this method needs more optimization in the laboratory to meet even higher requirements for industrial scale commercialization because of high cost and low efficiency.
At present, most of the commercially available 3-hydroxybutyric acid is a racemic mixture, with the ratio of (R)-3-hydroxybutyric acid to (S)-3-hydroxybutyric acid being about one to one. Although study showed that (S)-3-hydroxybutyric acid is not physiologically active, racemic 3-hydroxybutyric acid and its salts, especially sodium salts, are still the main commodity form and accepted by most consumers. It is expected that a single optical (R)-3-hydroxybutyric acid and its salts will become popular in future, replacing the racemic 3-hydroxybutyric acid and its salts.
Generally, it is believed that natural or biological compounds are safer (and non-toxic) than chemically produced compounds. People prefer the “natural” or “biological” feature of the source of pharmaceutical, food and cosmetic ingredients. For marketing purpose, pharmaceuticals, food, and cosmetics manufacturers are more willing to replace chemical process with biological process for making the same product. Therefore, there has been a goal to produce (R)-3-hydroxybutyric acid in a biological method instead of a chemical method which is the main method.